Menu Foods Limited, based in Streetsville, Ontario, Canada, is the largest maker of wet cat and dog food in North America, with its products sold under 95 brand names, which the company identifies as supermarkets, big box and pet product retailers and wholesalers.In March 2007, after numerous animals fell ill and died during quality-control tests, the company recalled over 60 million containers of food. Subsequent to the recall, the Animal Health Laboratory at the University of Guelph in Ontario, identified contaminants in some of the recalled food: aminopterin (a chemical used as rat poison), melamine (a plastic precursor that may also be used as a fertiliser), and cyanuric acid (which is commonly used to stabilise chlorine in swimming pools). If consumed by themselves, isolated doses of melamine or cyanuric acid should not cause health issues in pets. However, when these two chemicals are mixed together, an insoluble crystal is formed, that can rapidly obstruct the kidneys and cause renal failure. The incident has been labelled "one of the largest consumer-product recalls in North American history".